1. Field of the Invention
This invention relates to a ventilator for an elevator cage and more particularly to the ventilator wherein an active noise controller cancels noise entering into the cage.
2. Description of the Related Art
In recent years, an elevator for vertical transport has been required to provide higher speed and greater capabilities to meet the needs for super highrise buildings.
The elevator in a super highrise building has had many technical problems which previous elevators did not have. A representative problem is loud noise caused by changing air force between the elevator cage and a path to guide the cage. The noise is especially generated while the cage is moving at high speed. The noise enters the cage and makes passengers uncomfortable.
A ventilator with a silencer has been provided to block the noise around the cage from entering into the cage.
In this ventilator, as shown in fig.1 and fig.2, an exhaust fan 4 having a silencer 3 with sound-absorbing materials is installed on the top 2 of a cage 1.
Exhaust fan 4 introduces air into cage 1 through an air gate 6 formed around an illumination case 5 mounted to the top 2 and the noise generated by exhaust fan 4 is attenuated by silencer 3.
An exhaust aisle 7 formed to be similar to a labyrinth is provided at the lower part of cage 1.
FIG. 2 shows exhaust aisle 7 in detail. A first plate 8 having a plurality of obstacle sheets 8a is built on a board 1a of cage 1.
A second plate 9 is connected to the lower and outside part of a side board 1b of cage 1 with nut and bolt 10 so that first plate 8 is covered with second plate 9.
A plurality of obstacle sheets 9a are formed on second plate 9 and alternately provided against obstacle sheets 8a.
Exhaust aisle 7 is zigzag constructed by obstacle sheets 8a and 9a.
Exhaust aisle 7 exhausts the air from the cage 1 according to the stream of air shown by the arrow in FIG. 2. Noise on the outside of the cage may be blocked by obstacle sheets 8a and 9a.
The ventilator having silencer 3 with sound-absorbing materials and exhaust aisle 7 with obstacle sheets 8a and 9a is supposed to prevent noise from entering into cage 1, which is said to be passive noise control. However, the noise control may be limited.
There is especially noise around 125 Hz in cage 1, consequently it is important to attenuate such noise.
However, silencer 3 can not effectively restrain a low frequency range of noise (less than 500 Hz), for the low frequency noise has a long wavelength and is apt to penetrate the sound-absorbing materials. Further silencer 3 is restricted in size because silencer 3 is mounted on top 2 of cage 1.
Also, the construction of exhaust aisle 7 itself is complicated and its ability to efficiently attenuate the noise on the outside may be limited.
3. Summary of the Invention
It is an object of this invention to provide a ventilator for an elevator cage so as to provide a cage which is silent and comfortable for passengers to ride in.
In order to achieve this object and other objects readily apparent to those skilled in the art, there is provided a ventilator which has a supply fan mounted on a top of the elevator cage for supplying the air into the cage, a first duct for directing the air from the supply fan into the cage, sound-absorbing materials spread on an inside of the first duct for attenuating comparatively high frequency noise, and active noise control means for attenuating comparatively low frequency noise in the first duct.